Not to be an Ass, but have you double checked your rifle completely? I seem to recall a thread where a similar question was asked and it turned out the shop had installed the 10 MOA rail backwards, so instead of 10 MOA rail + 30 MOA mount, he ended up with 20 MOA total...
And I think your scope is junk.... but don't worry, I will take it off your hands for a "fair" value....
Not necessarily. You are assuming if you used a flat mount the scope would zero at the exact middle of the elevation range.
I assume you have zeroed the elevation turret for full turret movement to have full elevation available.
Removing the factory zerostop:
Ive have not done this, so you do this before zeroing?
Yes. Your "missing" elevation is in the video between the hard mechanical stop at 0:31 and the stop at 0:53
The procedure is on pages 22-23 of the manual.